1. Field
Polyurethanes, which are formed by reacting an isocyanate with a reactive hydrogen providing component, such as a polyol, have been widely used in preparing rigid and flexible foams, castings, adhesives and coatings. Typically, the reaction between the isocyanate and the polyol has been catalyzed by using various components such as amines, e.g. tertiary amines and organometallics, particularly organo tin compounds such as stannous octoate, dibutyl tin laurate, tin ethylhexanoate and so forth. The effectiveness of the catalyst is often measured by the cream time, which is the time required for the isocyanate and polyol syrup to turn from a clear solution to a creamy color; the gel time, which is the time required for polymer particles to form in the syrup; rise time, which is the time required for the syrup to rise to its maximum height; and cure time which is the time to reach a tack-free state.
In some applications for polyurethanes it is desirable to effect reaction in the shortest time possible and, therefore, pg,2 catalysts having tremendous activity are desired. In some applications, though, as in the molding of intricate parts or large objects, it may be desirable to keep the polyurethane composition in a fluid state for an extended time to permit the composition to completely fill the mold or flow into the cracks and crevices of the mold. Then, once the mold is completely filled, it is desirable to effect polymerization of the polyurethane in the shortest time possible so that the finished parts can be removed and the mold recharged with new materials. In this regard, it is desirable to delay the initial reaction, but after reaction commences then catalyze the polymerization rate. To do this it is necessary to extend the cream time to permit the polyurethane composition to penetrate the cracks and crevices in the mold and to extend the gelation time as the polyurethane foam on gelling becomes intractable and resists molding. However, once the reaction begins, it is desirable to end up with a rise and cure time comparable to those achieved by active catalysts as this will permit greater productivity.
2. Description of the Prior Art
Organometallics and particularly organo tin compounds such as tin ethylhexanoate, tin isooctoate, tin napthenate, di-n-butyl tin dilaurate; dibutyl tin diacetate, and tertiary nitrogen tin compounds such as dibutyl-tin-di(pyridine-4-carboxylic acid esters) as shown in U.S. Pat. No. 3,595,734; and U.S. Pat. No. 3,164,557 have been used to catalyze urethane reactions.
Amine compounds and particularly tertiary amines or their salts have been used as catalysts for polyurethanes. Examples of amines which are suited for catalyzing polyurethane reactions are dimethyl benzylamine, triethylenediamine, trimethylamine; alkanolamines such as diethanolamine, triethanolamine, N-diethyl-ethanolamine; N-hydroxyalkyl substituted imidazoles and N-vinyl pyrrolidone as shown in U.S. Pat. Nos. 3,645,927; 3,450,648; 3,448,065 and 3,746,663.
U.S. Pat. Nos. 3,620,986 and 3,580,868 show that Mannich bases of secondary amines and phenols can be used for catalyzing an isocyanate-hydroxyl reaction. Generally, some aminoalcohol is present and the phenol radical may contain an active hydrogen atom, e.g. COOH, CONH.sub.2, OH, etc., which can condense into the urethane structure. Typically, these Mannich bases are formed by reacting dimethylamine, formaldehyde, aminoalcohol and a phenol, e.g. Bisphenol A, or salicylic acid amide.
Although the above references indicate the compositions have catalytic activity, a number of references have suggested similar but different compositions as being useful as delayed action catalysts (DAC), i.e. those which initially delay and then catalyze the isocyanate-hydroxyl reaction. For example, chelating agents, e.g. beta-diketones and beta carbonyls with aminefree organometallics have been used. Examples of beta-diketones useful as a delayed action catalyst in polyurethane chemistry include 2,4-hexanedione, acetylacetone, 1,cyclohexyl-1, 3 butanedione; beta-hydroxy ketones, e.g. beta hydroxy quinoline, 1hydroxy-9-fluorenone, and alpha-hydroxy ketones, e.g. benzoin, acetoin and others as shown in U.S. pat. No. 3,635,906.
Another example of a delayed action catalyst for the preparation of foamed polyurethane resins is shown in U.S. Pat. 2,932,621. This patent discloses that amine salts of dicarboxylic acids and notably the hydroxy tertiary amine salts of oxalic acid are particulary effective in delaying the initial reaction between an isocyanate and hydroxyl group, but after an appropriate lapse of time, they become fully effective and cause the reaction to proceed to completion smoothly, rapidly and efficiently.
It has also been proposed to use quaternary ammonium salts of Mannich bases as a delayed action catalyst for the reaction between an isocyanate and polyol to form polyurethanes. Initially, the quaternary ammonium salt has little catalytic effect, but during the reaction it decomposes to form tertiary amine which can assist in catalyzing the reaction. Examples of quaternary ammonium salts of Mannich bases are shown in U.S. Pat. No. 2,950,262 and are prepared by reacting a secondary amine with an aldehyde and a ketone such as cyclohexanone and then reacting the Mannich base with an organic halide to form the quaternary ammonium salt.